Help, Rb26 Engine Is An 05U But Has No Serial Number

[NismoSTune]

I purchased an RB26 bare block which has 05U stamped on one side but there is no serial number on the other side, next to the RB26 stamp. I was told it was a Nur but I thought all Nur engines were N1?

Anyone know something about this?

[NismoSTune]

Won't get into the story but here's what I'm after. No opinions please, just facts so I don't get confused.

Here's the block tag (05U) Normally known as Standard block.

Here's the serial number location though there isn't one and it doesn't look like it was modified so to speak.

Here's where I may be confused. I thought the Nur engines were ALL N1 blocks (24U) but I was told this is a Nur block, something about having no serial number which in my mind all new blocks come with no serial number meaning this would be a simple standard block which didn't come in a car? Anyone know the facts?

Thanks.